Patent GB-396089-A (GB)
Title: Improvements in or relating to electric safety-lamps
IPC: F21V25/06
Filed: 1932-01-20
Abstract: 396,089. Electricbattery lamps. POLLOCK, S. A., Little Bush House, Kingsbury, London. Jan. 20, 1932, No. 1798. [Class 39 (ii).] A safety lamp comprises an electric-lamp bulb enclosed in an airtight chamber the pressure within which can be varied from that of the atmosphere surrounding the lamp so that a pressure operated switch within the chamber may be operated to break the circuit upon a predetermined alteration of the pressure in the air-tight chamber towards atmospheric pressure, and an externally operated switch also situated in the air-tight chamber and connected in series with the pressure-operated switch. The means for operating the former switch comprises a permanent magnet movably mounted outside the air-tight chamber and acting through a wall thereof upon a portion of the switch within the chamber. The air-tight chamber consists of a glass cylinder 15 with its upper and lower edges seated within grooves 16, 17 respectively provided in a brass cap 13 and a massive metal ring 34. Rubber packing within the grooves provides an air-tight joint. Bolts 12 between the cap 13 and ring 34 are provided with clamping-nuts 20, and extend through insulating-bushes 50 in a metal ring 42 formed on its upper face with an annular rib 43 engaging within an insulated groove containing a packing- ring 18 in the ring 34. A corrugated circular diaphragm 9 secured by a clamping-ring 49 and screws 33 to the underside of the ring 42, is also soldered to the latter to ensure an airtight joint. The centre of the diaphragm 9 carries a contact head 8 on a stem which extends through an insulating-bush 19 screwed into the centre of the ring 42, the adjustment of the diaphragm being such that, when the pressure within the air-tight chamber is greater than atmospheric the diaphragm is depressed and the contact head 8 is brought against the bottom 48 of a metal socket 45 within the insulating-bush 19 and closes the lamp circuit. Connection between the socket 45 and the centre contact of the lamp bulb is provided by a bolt 7 which serves to secure the bulb socket 6 upon the socket 45, insulating washers 46, 47 being interposed to prevent electrical connection between the two sockets. When the pressure within the chamber is less than atmospheric the diaphragm 9 is deflected inwardly, so that the contact head 8 is held in contact with a nut 40 on the lower end of the bolt 7. The breaking of the glass 15 causes the diaphragm to be restored to a neutral position, with the contact head 8 intermediate between the upper and lower contacts, thus breaking the circuit. The chamber may be either exhausted or filled with compressed air through a screw-threaded socket 25 connected by a passage 27 to a needle-valve controlled by a screwed plug 54. A flexible cable 31 connects one accumulator terminal to a screw 33 securing the diaphragm 9 in position, the other accumulator terminal being connected by a lead 32 to one of the bolts 12. The external switch controlling the circuit is mounted on the top 13 and comprises a semi-circular permanent magnet 1 disposed around a central boss and enclosed beneath a cover 24 formed with an arcuate slot for an operating-pin 26 which is mounted on one end of the magnet. Two plugs 2 of soft iron screwed into the cover 13 constitute pole pieces disposed above an armature 4 pivoted on the underside of the cover and insulated therefrom, the pivoting screw 52 serving also to secure a contact arm 5 extending downwardly into contact with the bulb holder 6. On moving the semi-circular magnet by means of its operating pin 26 the armature 4 may be raised into contact with the casing top to complete the circuit.